1. Field of the Invention
The present invention relates to a silver halide photographic emulsion and a photographic light-sensitive material containing this emulsion and, more particularly, to a silver halide photographic emulsion having a low fog and a high sensitivity and a photographic light-sensitive material containing this emulsion.
2. Description of the Related Art
Silver halide photographic emulsions for use in silver halide photographic light-sensitive materials are normally subjected to chemical sensitization using various chemical substances in order to obtain, e.g., desired sensitivities and gradations. Representative methods of the chemical sensitization are sulfur sensitization, selenium sensitization, noble metal sensitization using, e.g., gold, and combinations of these sensitization methods.
Recently, strong demands have arisen for a high sensitivity, a good graininess, and a high sharpness of a silver halide photographic light-sensitive material, and for rapid processing obtained by increasing, e.g., the rate of development of the material, and so various improvements have been made for the above sensitization methods.
Among the above sensitization methods, the selenium sensitization is disclosed in, e.g., U.S. Pat. Nos. 1,574,944, 1,602,592, 1,623,499, 3,297,446, 3,297,447, 3,320,069, 3,408,196, 3,408,197, 3,442,653, 3,420,670 and 3,591,385, French Patents 2,093,038 and 2,093,209, JP-B-52-34491 ("JP-B" means Published Examined Japanese Patent Application), JP-B-52-34492, JP-B-53-295, JP-B-57-22090, JP-A-59-180536 ("JP-A" means Published Unexamined Japanese Patent Application), JP-A-59-185330, JP-A-59-181337, JP-A-59-187338, JP-A-59-192241, JP-A-60-150046, JP-A-60-151637, JP-A-61-246738, JP-A-3-111838, JP-A-3-148648, British Patents 255,846 and 861,984, and H. E. Spencer et al., "Journal of Photographic Science," vol. 31, pages 158 to 169 (1983).
On the other hand, it is considered preferable in terms of uniformity of chemical sensitization and development properties that silver iodide (iodide ion) contents of individual silver halide grains be uniform in order to obtain a high sensitivity.
JP-A-2-68538 (Japanese Patent Application No. 63-220187) discloses a technique of eliminating a nonuniform halide distribution both inside each grain and between individual grains by using a halogen ion slow releasing agent or fine silver halide grains as a halogen ion supply source in place of a conventionally used aqueous halogen salt solution during formation of silver halide grains.
The above patent application, however, does not report that formation of silver halide grains performed while rapidly producing iodide ions is important in the manufacture of an emulsion with a high sensitivity and a low fog.
Generally, the selenium sensitization has a larger sensitizing effect than that obtained by the sulfur sensitization commonly performed in this field of art but often tends to increase fog and to readily cause soft tone. Although many of the above known patents are for improving these drawbacks, they can provide only unsatisfactory results so far. Therefore, a strong demand has arisen for particularly a radical improvement for suppressing generation of fog.
In addition, a significant increase in sensitivity can be obtained by especially when the sulfur sensitization or the selenium sensitization is combined with the gold sensitization, but also the fog increases at the same time. The increase in fog in gold-selenium sensitization is larger than that in gold-sulfur sensitization. So development of a technique capable of suppressing generation of fog has been strongly desired.